Creep failure behaviour of a circumferential P91 pipe weldment with an anisotropic weld metal subjected to internal pressure and end load

Abstract

The creep failure behaviour of a P91 pipe weldment that has an ‘anisotropic’ weld metal (WM), under internal pressure and end load, was investigated using the finite-element (FE) method. It is assumed that the WM consists of a columnar region and a weaker equiaxed (fine-grained and coarse-grained) region. A practical pipe weld and bead dimensions were used for the FE model. Creep damage analyses were conducted using a single-variable, Kachanov type damage law, for which the material properties used were determined on the basis of the experimental data. Life prediction was also performed using a steady-state approach. Three representative cases, i.e. ‘matched’, ‘under-matched’, and ‘over-matched’, with respect to WM strength, were considered. Failure lives and failure positions of the weldment, for various cases, were investigated. The results were compared with those obtained from the corresponding weldment with an isotropic WM, from which the effects of the WM anisotropy on the failure life and failure location can be evaluated.